| Nowadays, rapid developments of high date rate satellite communication, localpoint-to-multipoint communication and millimeter wave imaging technologies havebeen leading to strict requirements for multi-beam antennas. Traditional multi-beamantennas, such as parabolic reflector antenna and phased array antenna, have eitherlimited scan coverage and poor beam uniformity, or narrow bandwidth, high losses,complicated and expensive phase-shift network, which can not meet the needs of lowcost and efficient millimeter wave communication systems. Lens, in the field of opticalimaging and focusing, has the capability of converting different kinds of divergentenergy into planar waves, which greatly enriches multi-beam antenna design. Lensantennas often have many attractive features such as low cost, broad bandwidth, widemulti-beam scan coverage and simple feed network. However, they still have someshortcomings, such as their large size and heavy weight especially at lower frequencies.Meanwhile, unstable composite material technologies have greatly hindered thedevelopment of lens antennas for a long time. Therefore, it is particularly necessary tocarry out studies on multi-beam lens technologies, including the theories, analysismethods, design, experiments and applications, so as to make the best of its potentialtechnical advantages.For these purposes, a number of studies on multi-beam lens antennas are carriedout in this dissertation. The studies include basic principles and analysis methods of lensantenna, fast calculation and efficient optimization design of electrically large sizemulti-beam lens antenna, multi-objective and multi-scaling optimization design of lensantenna, novel feed arrays and multi-beam scanning properties of lens antenna,multi-beam lens antennas using high impedance surfaces, and use of lens antenna inshipborne multi-beam satellite communication and tracking systems, etc. The maincontent of this dissertation are as follows:1. Domestic and international relevant research backgrounds and progresses ofmulti-beam lens antennas are introduced. Then, main classification and basic principlesare described; and some typical analysis and design approaches are reviewed, includingthe geometrical optics/physical optics methods, full wave analysis method, and exactanalytical solution of special shaped lens. In addition, a Luneburg lens antenna (LLA) is taken as an example to describe its radiation mechanism. Finally, some implementationtechniques of LLA are compared and investigated.2. Near-field aperture distributions of practical feed models are for the first timetaken into account in the lens antenna optimization with structural parameters of thelens. In this way, the radiation characteristics of practical feed-lens system can beaccurately evaluated and efficiently designed. This is especially feasible for the optimaldesign of electrically large size lens antenna. Meanwhile, the convergence rate andglobal optimum solution of the design procedure are analyzed. An investigation of theinfluences of the various lens-to-feed distances as well as aperture sizes of lens antennaon the aperture efficiency for a less-layer design is also proposed. Moreover, theradiation characteristics of lens antenna fed by arbitrary near-field distributions of feedsare described. Finally, the design, fabrication and measurement of electrically large andefficient lens antenna with minimum number of layers are detailed, and this designgreatly reduces the complexity of manufacturing processes.3. In the multi-band lens antenna design, goals of maximizing aperture efficienciesat separated frequency bands simultaneously and keeping the sidelobe envelope lowerenough contradict with each other. A multi-objective and multi-scaling optimizationalgorithm is firstly adopted for the optimal design of LLA. Two typical examples arepresented to verify the design procedure. The first example is to maximum apertureefficiency at each frequency band, and the other one is to achieve high gain and keepthe sidelobe level lower enough over one frequency band. Compared with previousworks obtained by single objective optimization algorithm, the proposed designprocedure provides much better radiation performances. Many Pareto-optimizationsolutions can be obtained in a single run without the need of selecting the weightingfactors. The proposed method offers great design freedom to the designers. They canchoose the Pareto-optimal solutions as needed.4. An innovative design concept of four dimensional antenna arrays is firstlyintroduced in the circular antenna arrays for the feed array design of lens antennas. Fourdimensional circular antenna arrays with low amplitude excitation dynamic-range ratiosor even uniform amplitude excitations can be used to synthesize low and equal-ripplesidelobe patterns (-45dB), flat-topped patterns and scanning sum beams without anypattern deterioration, and also suppress sidebands radiation. This design greatlysimplifies the array feed network. In addition, LLA can be used to launch multiple beams by implementing a semicircular array of Vivaldi antenna elements at theperiphery of the lens. A scan coverage of178o with-3dB beam crossover is achieved inthe desired frequency band.5. The research background of high impedance surfaces is briefly reviewed. Thetransmission characteristics, radiation mechanism, and promising application of highimpedance surfaces are also described. Then, several kinds of novel high impedancemetallic cells are proposed, including slotted metallic cells, capacitively-loaded stripmetallic cells and bended-arm metallic cells. The surface impedance and localdispersion characteristics of these cells are also investigated. Based on thesecharacteristics, the variable surface impedance technique is adopted for the lens antennadesign. The local dispersion characteristics, phase velocity and propagation paths ofsurface waves are controlled by gradually changing geometrical parameters of metalliccells. In this way, the necessary refractive index distribution of the lens is achieved.Finally, a low profile, lightweight and efficient planar half Maxwell fish-eye (HMFE)lens antenna is optimally designed. Both radiation performance of single beamconfiguration and wide multi-beam scanning properties of multiple-beam configurationare characterized and experimentally verified. The proposed approach and unit cellmodels are especially feasible for lens antennas with index gradient varying in a largerange and have good universality.6. A shipborne multi-beam satellite communication and tracking system based onLLA is presented. A half LLA prototype is adopted for tracking several geosynchronoussatellites simultaneously. The tracking performances of half LLA and LLA are alsocompared and investigated. The proposed tracking system meets the requirements ofshipborne multi-beam satellite communication system. It has a major advantage ofreplacing at least three parabolic reflector antennas and occupying less ship space. Inaddition, a satellite network communication solution based on half LLA arrays ispreliminarily proposed. Finally, the ground tracking satellites experiment verified theeffectiveness and feasibility of the proposed tracking system. The results show that the2-beam half LLA tracking system prototype can receive two geosynchronous satellitesignals simultaneously. |
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